Windows does not have the concept of "time_t". The C runtime in
use does.
We use the DigitalMars C runtime for the 32-bit model, which is
the default one. The Microsoft one is used for 64-bit and 32-bit
COFF. I'm not sure how the MS C library deals with time_t,
however the time() function (as exported from the library file /
DLL) is the 32-bit version. If I were to guess, the C headers
define a macro which redirects time() calls to the 64-bit version
when appropriate. The D bindings don't copy that behavior.

If I were to import the time() function from MSVCR*.dll, what
size its return value would be?

MSVC runtime dll doesn't export `time` function, it exports
_time32 and _time64. `time` is a wrapper in the import library,
its time_t is probably 32-bit for binary compatibility with code
compiled before VC2005 that first migrated to 64-bit time_t by
default.

Windows does not have the concept of "time_t". The C runtime in
use does.
We use the DigitalMars C runtime for the 32-bit model, which is
the default one. The Microsoft one is used for 64-bit and 32-bit
COFF. I'm not sure how the MS C library deals with time_t,
however the time() function (as exported from the library file /
DLL) is the 32-bit version. If I were to guess, the C headers
define a macro which redirects time() calls to the 64-bit version
when appropriate. The D bindings don't copy that behavior.

The VS C runtime uses a macro to indicate whether time_t should be treated
as 32-bit or 64-bit on 32-bit systems. I thought that the default was
32-bit, but it looks like it's actually 64-bit, with the macro being
_USE_32BIT_TIME_T.
https://msdn.microsoft.com/en-us/library/1f4c8f33(v=vs.140).aspx
I guess that that the correct way to handle that would be to make it so that
druntime defines it as 64-bit by default and then has a version identifier
to change the behavior, but I don't know how that sort of thing has been
handled with the Win32 stuff in general. In the case of the stupid
unicode-related macros, IIRC, the solution is to just force you to use
either the A or W functions explicitly (preferably the W functions) rather
than making either of them the default or using a version identifier. That
approach really isn't an option here though, since the names don't changee
but rather the types.
- Jonathan M Davis